You are looking at a printed calendar for a given month. The weeks are in rows. Each day is a square on the calendar. You draw a three-by-three square around nine dates. You notice that the sum of these dates is divisible by . What is the date in the lower-right corner of your three-by-three square?

Source: mathcontest.olemiss.edu 8/27/2012

SOLUTION
There are eleven three-by-three squares that contain dates.
Sum . NO, not divisible by .